Fecal cortisol metabolites to assess stress in wildlife: Evaluation of a field method on free ranging chamois.

Measuring fecal glucocorticoid metabolites (FCM) has become a widely utilized technique to assess stress and to explore adrenocortical activity in various species. However, when applied in free ranging wildlife populations several endogen, environmental and methodological factors may substantially affect FCM levels. The aim of this study was to determine the impact of the factors sex, individual differences, storage conditions and distribution of metabolites in the feces on final results when using samples of unknown individuals. A free ranging Alpine chamois population in the Salzkammergut, Austria, was sampled from June to October 2011 and FCM were analyzed with an enzyme immunoassay. For assay validation a high performance liquid chromatography was performed. The effect of storage conditions on metabolites was tested with two storage experiments and the distribution of metabolites in the feces was investigated by the analysis of aliquots of single fecal samples. The possible effect of individually different FCM levels and variable reactions to stressful events were evaluated with a simulation experiment. A highly significant seasonal trend (p<0.001) as well as a considerable variance of individual FCM levels within the population sampled from June to October was found. Storage time, distribution of metabolites in the feces and individual differences are demonstrated to influence FCM levels, with the latter being the confounding factor of prime importance. Simulations confirmed that individual reactions to stressors in terms of varying gradients and FCM levels can explain the observed FCM patterns. Our data indicate that not a single variable but a combination of influencing factors modulates the observed pattern and variation. These factors, above all individual differences in FCM excretion, may inevitably jeopardize meaningful interpretation of data if unknown individuals of a population are sampled.